As an example of a feedback channel for Automatic Repeat reQuest (ARQ), there has been a feedback channel employed in High Speed Downlink Packet Access (HSDPA) (see Non-patent Publication 2, for example).
In HSDPA, Code Division Multiplexing (CDM) is applied to High Speed Physical Downlink Shared Channel (HS-PDSCH), which is a physical channel for transmitting traffic data, thereby enabling simultaneous data transmissions to plural mobile stations per Transmission Time Interval (TTI). Therefore, High Speed Dedicated Physical Control Channels (HS-DPCCH), which are control channels for sending back to a sender ACK/NACK information (an ARQ feedback signal) as a decoding result of a data channel transmitted through the HS-PDSCH, are also simultaneously sent back from the plural mobile stations.
The HS-DPCCH is a dedicated physical channel spread by a mobile station specific scramble code in order to recognize the ARQ feedback signals from corresponding plural mobile stations. Therefore, while the HS-DPCCH is allocated to a certain mobile station, a physical channel parameter such as the scramble code specifically for transmitting the ARQ feedback signal is not necessarily re-allocated, and information on the allocated physical channel is not required to be sent.
FIG. 1 shows an example of the HS-DPCCH, which is the physical channel for transmitting the ARQ feedback signal in HSDPA. In the HS-DPCCH, a set of control information is transmitted using three time slots. In addition, the HS-DPCCH is code-multiplexed with other physical channels in order to transmit the data channel and the like for an uplink transmission. The code-multiplexed signal sequence undergoes spreading using the user-specific scramble code, and is transmitted.                Non-patent Publication 1: 3GPP TS25.308        Non-patent Publication 2: 3GPP TSG-RAN#26 RP-040461        